This invention is an improved method and apparatus for establishing and maintaining a fluid seal on a well.
Reliability, safety, and ease of maintenance are among the most important considerations in the design of a fluid seal for a pumping valve on a well head. Fluid sealing apparatus, sometimes known as "stuffing boxes", seal a well by providing a packing material in close association with a polished rod. The sealing apparatus typically contains packing material that forms a fluid resistant barrier at the interface of the packing material and polished rod. The polished rod reciprocates in and out of the sealing apparatus. A stuffing box contains "stuffing" or packing, which prevents the leakage of hydrocarbons or other fluids during operation of a well.
There are several types of stuffing boxes. Some stuffing boxes use opposing rams which close upon the surface of the polished rod from two or more directions, thereby encircling the polished rod and forming a seal. Other types of stuffing boxes contain cone-shaped packing material that is stacked within the housing of the stuffing box. The packing in "cone-type" stuffing boxes comprises a stack of funnel-shaped packing discs that are forced into close association with the polished rod by mechanical devices such as bolts, adjustment screws, and the like.
In both ram-type and cone-type stuffing boxes, the packing material typically is forced into engagement with the polished rod by manually engaging alignment apparatus. In some cases, hydraulic pressures are used to force the packing material into close association with the polished rod, thereby sealing the well.
Many stuffing boxes contain relatively complex bolting arrangements, which may include alignment bolts or other mechanical devices on the exterior of the stuffing box. Stuffing boxes are easily damaged, because they are located in the relatively harsh environment above a wellhead. Oil field workers use heavy tools and machinery in the immediate vicinity of stuffing boxes. Work on wells may be performed at night or during conditions of low visibility, making it difficult to avoid damaging stuffing boxes. Parts extending from the surface of stuffing boxes easily can be damaged. If a stuffing box is damaged, the seal may be broken, allowing oil or other corrosive fluids to escape from the well, causing environmental and safety hazards.
Maintenance of stuffing boxes is expensive. It is costly to dispatch personnel to a well site to replace and/or maintain the sealing arrangement of a stuffing box. Further, when a stuffing box must be replaced or maintained, production from the well must be temporarily discontinued, reducing profits from the well.
Conventional methods of replacing packing materials inside stuffing boxes include disassembly of the stuffing box by unbolting, unlatching or otherwise releasing mechanical or hydraulic fasteners. Upon such disassembly, the packing materials are replaced with new materials, and the stuffing box is reassembled. The time required and frequency of replacement of packing materials is an important factor in the quality of the results achieved with a particular stuffing box. A stuffing box that facilitates easier maintenance is desirable.
In some cases, a stuffing box may be misaligned with the polished rod extending into the stuffing box. Misalignment can result in excess friction of the polished rod with the stuffing box, causing undesirable heat. This friction may provide a safety hazard and increased risk of fire or failure of the stuffing box. Further, such friction may deform a polished rod, requiring its replacement. In some cases, misalignment of a stuffing box reduces the pressure exerted in withdrawing fluids from the well, decreasing production. Misalignment causes premature deterioration of packing materials. Stuffing boxes that require adjustment of alignment bolts or other alignment devices may become misaligned during operation due to failure, weakening, or loosening of such alignment mechanisms.